Collapse of polymer brushes grafted onto planar ... - Wageningen UR

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MEAN-FIELD THEORY PREDICTION OF PHASE BEHAVIOR OF ABC TRIBLOCK COPOLYMER IN SELECTIVE SOLVENT N.P. Shusharina 1) , P. Alexandridis 1) , S. Balijepalli 2) , H.J.M. Gruenbauer 3) 1) Department of Chemical Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, U.S.A. 2) New Product & Mathematical Modeling Group, Corporate R&D, The Dow Chemical Co., Midland, MI 48674, U.S.A. 3) New Business Development, Dow Benelux N.V., 4530 AA Terneuzen, The Netherlands email: ns33@eng.buffalo.edu ABSTRACT A mean-field lattice theory is applied to predict the self-assembly into ordered structures of ABC triblock copolymers in selective solvent. More specifically, the composition-temperature phase diagram has been constructed for the system (C)14(PO)12(EO)17/water, where C stands for methylene, PO for propylene oxide and EO for ethylene oxide. The model predicts thermotropic phase transitions between the ordered hexagonal, lamellar, reverse hexagonal, and reverse cubic phases, as well as the disordered phase. The thermotropic behavior is a result of the temperature dependence of water interaction with EO- and POsegments. The lyotropic effect (caused by changing the solvent concentration) on the formation of different structures has been found weak. The structure in the ordered phases is described by analyzing the species volume fraction profiles and the end segment and junction distributions. A "triple-layer" structure has been found for each of the ordered phases, with each layer rich in C-, PO-, and EO-segments, respectively. The electrolyte effects on the macroscopic phase behavior are also considered. The addition of NaCl is found to sharpen the thermotropic phase transition and shift them to lower temperatures compared to the salt-free case. The parameters describing interactions between different species are obtained from simple experiments, and thus this model can be useful in capturing the effects of various electrolytes on non-ionic surfactants phase behavior.
PROTEIN ADSORPTION ON SURFACES WITH GRAFTED POLYMERS Igal Szleifer Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA email: igal @ purdue.edu ABSTRACT Introduction Protein adsorption plays a key role in a variety of biological processes and it is very important in many biotechnological processes. For example, when a foreign body is put in contact with the blood stream, large blood proteins e.g. fibrinogen, adsorb to the surface of the material. This protein adsorption is necessary for the following adhesion of platelet and the possibility of surface induced thrombosis. It has been shown that when the surface adsorption of fibrinogen is below a certain threshold, platelet adhesion does not occur. Therefore, one of the important steps in increasing biocompatibility in a material is by preventing the adsorption of blood proteins into the surface of the material. Another important example in which protein adsorption plays a key role is in the design of biosensors. In some of these cases it is necessary to obtain an ordered array of enzymes. Further, the proteins should adsorb in their biological active conformation for proper functioning of the device. These two examples show the importance of protein adsorption. However, in one case it is necessary to induce protein adsorption while in the other it is important to prevent the adsorption of the macromolecules. Protein adsorption is a very complex process since it involves very large energy scales. Typical van der Waals interactions between surfaces and proteins are in the order of tens to hundred times the thermal energy. Further, proteins are highly heterogeneous molecules that have the ability to change their conformation upon adsorption on the surface. This change of conformation is induced by the presence of an inhomogeneous interaction field due to surface. Another complexity arises from the fact that in general proteins have charged amino acids and therefore electrostatic interactions play a key role on the adsorption behavior. In this talk we will discuss the ability of grafted polymer layers to control protein adsorption. This is aimed to use grafted polymers as surface modifiers that can be tuned to prevent protein adsorption or in other cases to control the kind of protein conformation that adsorbs on the surface. We will show our theoretical studies of how different types of grafted polymers can be used to tune the adsorption process. Our theoretical approach is based on a generalization of a molecular mean-field theory that has been very successful to describe the properties of tethered polymers. For example, the theory is capable to quantitatively describe the pressurearea isotherms of polystyrene-poly ethylene oxide (PS-PEO) diblock copolymers spread at the water-air interface. We have also shown that the predictions of the theory are in excellent quantitative agreement with experimental observations of the structure of PEO molecules grafted on surfaces with rigid collagen molecules. Furthermore, we will also show that the predictions of the theory are in very good agreement with experimental observations for the adsorption isotherms of lysozyme and fibrinogen on surfaces with grafted PEO. These comparisons have been done over a very large range of polymer chain length, from short oligomers to long PEO molecules. Thermodynamic vs. Kinetic Control of Protein Adsorption Due to the very large energy scales involved on the adsorption of proteins it is important to understand the equilibrium and kinetic process. When a surface is modified by grafting polymer molecules the modified surface-protein interactions give rise to changes in both the kinetics of adsorption as well as the equilibrium amount of proteins adsorbed. The question is then what type of control is necessary depending on the type of
Page 1 and 2: Frontis - Wageningen International
Page 3 and 4: Prof. dr. Hans Fraaije Leiden Unive
Page 5 and 6: Prof. Ullrich Steiner University of
Page 7 and 8: Preface Self-consistent field model
Page 9 and 10: covered by polymers), and R. Rajago
Page 11 and 12: FIRST-ORDER WETTING TRANSITION AT F
Page 13 and 14: MOLECULAR SCF MODELLING OF PORES IN
Page 15 and 16: COLLAPSE OF POLYMER BRUSHES GRAFTED
Page 17 and 18: SURFACE FORCES, SUPRAMOLECULAR POLY
Page 19 and 20: SWEET BRUSHES: SYNTHESIS AND INTERF
Page 21 and 22: EFFECT OF MIXING OF TWO CHARGED PHO
Page 23 and 24: Figure 2 show a semi-log comparison
Page 25 and 26: MODELING OF STATIONARY POLYMER DIFF
Page 27 and 28: THEORY AND SIMULATION OF BILAYER ME
Page 29 and 30: Figure 1. Time evolution of the she
Page 31 and 32: SALT EFFECT TO RAYLEIGH DROPLETS OF
Page 33 and 34: MACROMOLECULES AT INTERFACES, A FLE
Page 35 and 36: APPLICATION OF HETEROGENEOUS LATTIC
Page 37 and 38: 8. Linse, P., 1993b. Phase behavior
Page 39 and 40: MODELING INTERFACIAL EFFECTS ON THE
Page 41 and 42: Using this patterned electrode, we
Page 43 and 44: span the gap between the electrodes
Page 45 and 46: desirable to use a probe with a muc
Page 47 and 48: span the gap between the electrodes
Page 49 and 50: MEMBRANE FUSION: RESULTS FROM SIMUL
Page 51: the transition temperature T * when
Page 55 and 56: MODELLING STRUCTURE AND ADHESION AT
Page 57 and 58: References 1. Fischel, L.B. and The
Page 59 and 60: MULTIDOMAIN CONFORMATIONS OF RANDOM
Page 61 and 62: SUPRAMOLECULAR COORDINATION POLYMER
Page 63 and 64: INFLUENCE OF POLYMERS ON THE BENDIN
Page 65 and 66: SPINODAL DECOMPOSITION IN BINARY PO
Page 67 and 68: PERSISTENCE LENGTH OF WORM-LIKE MIC
Page 69 and 70: For small particles with radius R <
Page 71: MEAN-FIELD THEORY FOR THE ADSORPTIO

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